This study is designed to determine whether monthly injections with Synagis reduce symptoms of RSV infection, hospitalization, use of pulmonary medications, and colonication with pseudomonas aeruginosa. A control group of children who get a sterile salt-water injection instead of study drug is necessary in order to detect favorable effects of Synagis. This is a randomized, double-blind, placebo-controlled trial. Children will get either Synagis or placebo-given by a shot in the thigh or arm muscle. Each child will have 1:1 (50%) chance of getting Synagis or placebo.